The invention at hand relates to blow-molded fuel tanks for vehicles in general, and fuel tanks with a heat shield in particular. The invention at hand also relates to a blow-molding method for producing a fuel tank with an integrated heat shield.
Today, fuel tanks for motor vehicles usually are produced by blow-molding using low-pressure polyethylene, i.e., high-density polyethylene (HDPE). The use of this type of plastic material results in long-lasting and solid fuel tanks which are also corrosion-resistant and can be produced simply and at low cost even while adhering to very exact specifications. However, such fuel tanks manufactured from this material have the disadvantage that they have a relatively low melting point. The melting temperature of this material is, for example, so low that the heat of the exhaust pipe or exhaust system of the motor vehicle could easily burn a hole into the tank or have another disadvantageous effect on it.
It is therefore necessary that a heat shield be installed between the fuel tank and the exhaust system for a fuel tank made from this material and located near the exhaust system or exhaust pipes. The state of the art discloses numerous methods of arranging a heat shield in a suitable position or a suitable place in order to protect fuel tanks from the heat of exhaust systems. For example, the installation of a heat shield near the vehicle bottom without direct contact to a fuel tank as well as the attachment of a heat shield to the tank has been described. Heat shields of this type are typically pressed parts of steel, SMC molding masses or duroplasts or heat-resistant compounds. However, such heat shields used to protect fuel tanks require longer production times, additional setup work and additional material or parts, along with the associated cost increases. In practice, it was also found that such heat shields may detach during the life of the vehicle because of corrosion, the effects of lose road surface, such as asphalt or gravel, and impacts because of poor road conditions or rough road surfaces. Examples of such heat shields as protection for a vehicle motor are described in U.S. Pat. No. 4,930,811 and U.S. Pat. No. 4,909,530 as well as U.S. Pat. No. 5,656,353.
An example of a heat shield attached directly to a fuel tank is disclosed in U.S. Pat. No. 5,193,262. Another example of direct attachment of a heat shield to a fuel tank is described in the three patents U.S. Pat. No. 5,188,981, U.S. Pat. No. 5,308,571, and U.S. Pat. No. 5,674,603, in which a heat shield is attached during the molding process to the outside of a tank and is integrated with it. Another example of an integrated heat shield is disclosed in U.S. Pat. No. 5,129,544, in which a very thin metal foil, for example of aluminum, is joined by heat and pressure with addition of an adhesion promoter between an outer plastic layer and an inner plastic layer.
The state of the art describes two kinds or types of heat shields that may be joined together in a laminate and may be integrated with the tank. The person skilled in the art knows, for example, the reflective type in which a reflecting metal, such as aluminum, is used, and an insulting type that uses, for example, a polymer foam or a plastic. In some examples of the state of the art, for example in the previously mentioned three U.S. patents, U.S. Pat. No. 5,188,981, U.S. Pat. No. 5,308,571, and U.S. Pat. No. 5,674,603, the laminate consists of a metal foil with a thickness of about 1 to 2 mils (1 mil=25.4 xcexcm), and a layer of a non-porous, insulating material and a layer of a porous, insulating material. These laminate layers are chemically interconnected. In U.S. Pat. No. 5,567,296 and U.S. Pat. No. 5,547,096, the outer, reflective layer is an electrochemically applied metal.
Although a fuel tank with an integrated heat shield, such as, for example, in the mentioned U.S. Pat. No. 5,188,981, U.S. Pat. No. 5,308,571, and U.S. Pat. No. 5,674,603, appears to be the best solution, it was found that in practice the laminate layers of the heat shield of such fuel tanks have a tendency to peel off or break off or completely detach over the course of time because of wear due to heat, chemicals, and/or vibration. In particular, it was found that in practice it is difficult to bond the outer metal foil to the inner, insulating layers.
In the exemplary embodiments of the state of the art, in which an electrochemically applied metal is used, it is also difficult to obtain a layer with a sufficient thickness at an economical price. Practice has also shown that layers produced in such a way tend toward losses due to abrasion.
As a result, there is a need for an economical, easily producible, easily moldable, and long-lasting or wear-resistant fuel tank that can be located close to the exhaust system of the motor vehicle without being damaged.
It is a further objective of the invention at hand to create a fuel tank with an integrated heat shield. In particular, a fuel tank should be created whose integrated heat shield does not peel off, break off, or completely detach from the tank, but whose heat shield is integrated permanently in the tank and is bound in a fixed and definitive manner to the tank.
It is yet another objective of the invention at hand to create a process that can be used to manufacture fuel tanks with integrated heat shields economically, simply, and in a short time. In particular, a process should be created that makes it possible to achieve a permanent and extremely effective integrative bond of the heat shield to the fuel tank in a quick and cost effective manner.
The invention at hand provides a way of eliminating the mentioned disadvantages of the state of the art by utilizing the advantages of blow-molding in manufacturing the fuel tanks while simultaneously providing a versatile, easily positioned, easily producible heat shield that can be integrated permanently or in a wear-resistant manner. The invention at hand also uses the advantages associated with the use of a relatively thick, metallic heat shield as an integrating component of a blow-molded fuel tank. The invention at hand furthermore utilizes the advantages associated with a metallic heat shield cast directly into the wall of the fuel tank at any desired position.
In a preferred method for producing a fuel tank according to the invention at hand, a relatively thick, metal sheet is perforated in such a way that a plurality of protrusions/break-through in the form of claws or barbs is created, and this metal sheet is reshaped into a desired configuration or shape.
The reshaped, metal sheet and a parison are then placed in an opened mold that is suitable for blow-molding. After the mold is closed, the mold chamber is heated and a pressurized fluid is introduced into the parison in such a way that the latter expands and comes into contact with the inside walls of the mold, and the placed, perforated, and shaped metal sheet is pressed into the wall of the parison. The mold is then opened, and the finished fuel tank is removed from the mold along with the embedded heat shield. A fuel tank according to the invention at hand comprises a perforated, shaped, metal sheet whose protrusions are cast directly into the wall of the tank, and which metal sheet is located close to a heat source, such as, for example, components of the exhaust system, when the tank is installed.
The invention at hand has additional advantages: a heat shield is bonded permanently and firmly to the outside of the tank wall. This also means that neither additional assembly nor additional or later work steps are required. The heat shield also can be positioned accurately and precisely. It is advantageous that no additional time is required when the mold suitable for blow-molding is used, but only the so-called xe2x80x9cin-moldxe2x80x9d time required when producing an adequate fuel tank without integrated heat shield. Another advantage is that the preshaped heat shield can be configured so that it adapts itself to any contour during the blow-molding of the three-dimensional tank body.
According to an exemplary embodiment of the invention, a blow-molded fuel tank for a motor vehicle that comprises a container and a heat shield is created. The container has at least one wall and is made from a thermoforming, polymer plastic that is suitable for blow-molding. The heat shield is provided on at least one of the walls and integrated therein. The heat shield is constructed as a three-dimensional body with a first side and a second side, and has a plurality of perforations. The perforation density is usually about 50 perforations per 10 cm2. These perforations are all made from the same side, so that all claws are formed on the side of the heat shield. In the finished fuel tank, a peg consisting of the same plastic as the container extends through each perforation. The claw is embedded into the wall of the container in such a way that the heat shield is integrated with the container.
In a preferred embodiment of the invention at hand, a method for producing a fuel tank with a container and a heat shield is created. The container is hereby defined by at least one wall, where said wall has an inside and an outside. The heat shield is embedded into the outside of the wall. In the first step of the process, a metal sheet with a thickness between 0.1 mm and 0.3 mm is provided, and a plurality of perforations are shaped into the metal sheet from the same side in such a way that protrusion-like claws are formed on the other side of the metal sheet. The metal sheet is constructed as a three-dimensional shape and is then arranged in a chamber of a blow mold with inside walls, where said inside walls define the outside shape of a fuel tank to be blow-molded. The metal sheet is arranged in such a way that its claws extend into the chamber of the blow mold. A parison with an inner chamber is then arranged inside the chamber of the blow mold. A pressurized fluid is introduced into the inner chamber of the parison. The fluid is under a sufficient pressure to bring the parison into contact with the chamber of the blow mold and into contact with the metal sheet and its claws, in such a way that the plastic places itself around the claws of the perforations, and in particular projects through the protrusions. In this manner, the metal sheet is interactively fastened to the plastic of the tank body. The expanded or enlarged parison is then hardened, and the produced, blow-molded fuel tank is removed from the chamber of the blow mold with an integrated, metal heat shield.
The blow-molded fuel tanks naturally could comprise several layers.